This study investigated the relevance of different lexical processing strategies for vocabulary acquisition during a reading-for-comprehension task involving fifty-six English learners in a local Chinese university. Both cognitive processes and incidental vocabulary acquisition have been extensively studied. However, few studies have directly explored the underlying cognitive mechanisms of incidental vocabulary acquisition. The present research attempted to experimentally test the influence of different lexical processing strategies on incidental vocabulary acquisition while reading. The strategies which learners adopted to deal with unknown lexical items were analyzed with regard to the cognitive processes involved, namely the explicit/implicit cognitive process and the top-down/bottom-up cognitive process. A mixed research method was adopted to achieve the research purpose. The principal research instruments for data collection were an unknown vocabulary extraction task, a reading-for-comprehension task, a think-aloud protocol, and a vocabulary retention test. Based on introspective data gathered through the think-aloud task and the results of vocabulary retention test, the researcher discussed the characteristics of different cognitive processes involved in incidental vocabulary acquisition. The research found that there were mainly four types of lexical processing strategies and two sub-strategies of the inference strategy. The implicit processing strategy could lead to incidental vocabulary acquisition, though its acquisition effect was not as good as that of the explicit ones. The explicit cognitive process could induce more involvement load and deeper cognitive processing, thus helping learners to construct form-meaning combinations. The acquisition effect of the bottom-up lexical processing strategies was much better than that of the top-down ones. The meaning of a word obtained through a top-down cognitive approach is embedded in the contextual environment and can easily be lost without the related context. Finally, a multilayered cognitive model has been developed, which offers both theoretical and practical implications for teachers and students in Chinese colleges and universities.